As an example of a wireless communication system to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) (hereinafter, referred to as ‘LTE’) communication system is briefly described.
FIG. 1 is a view schematically illustrating the network architecture of an E-UMTS as an exemplary wireless communication system. An Evolved Universal Mobile Telecommunications System (E-UMTS) is an advanced version of a legacy Universal Mobile Telecommunications System (UMTS) and standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as an LTE system. For details of the technical specifications of UMTS and E-UMTS, reference can respectively be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs (eNBs), and an Access Gateway (AG) which is located at an end of a network (Evolved-Universal Terrestrial Radio Access Network ((E-UTRAN)) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.
One or more cells may exist in one eNB. A cell is configured to use one of bandwidths of 1.25, 2.5, 5, 10, 20 MHz to provide a downlink or uplink transport service to several UEs. Different cells may be configured to provide different bandwidths. The eNB controls data transmission and reception for a plurality of UEs. The eNB transmits downlink scheduling information for downlink data to notify a corresponding UE of a data transmission time/frequency domain, coding, data size, and Hybrid Automatic Repeat and reQuest (HARQ)-related information. In addition, the eNB transmits uplink scheduling information for uplink data to inform a corresponding UE of available time/frequency domains, coding, data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A Core Network (CN) may include an AG and a network node for user registration of the UE. The AG manages mobility of the UE on a Tracking Area (TA) basis, wherein one TA consists of a plurality of cells.
Although radio communication technology has been developed up to LTE based on Wideband Code Division Multiple Access (WCDMA), demands and expectations of users and service providers have continued to increase. In addition, since other radio access technologies continue to be developed, new technical evolution is required for future competitiveness. Decrease of cost per bit, increase of service availability, flexible use of a frequency band, simple structure and open interface, and suitable power consumption by a UE are required.